I can’t help but feel that NLP is once again stuck.
From about 2011 to 2019, I can identify a huge step forward just about every year. But the last thing that truly excited me is BERT, which came out in 2018 and was published in 2019. For those not in the know, the idea of BERT is to pre-train a gigantic language model, with either monolingual or multilingual data. The major pre-training task is masked language model prediction: we pretend some small percentage (usualyl 15%) of the words in a sentence are obscured by noise and try to predict what they were. Ancillary tasks like predicting whether two sentences are adjacent or not (or if they were, what was their order) are also used, but appear to be non-essential. Pre-training (done a single time, at some expense, at BigCo HQ), produces a contextual encoder, a model which can embed words and sentences in ways that are useful for many downstream tasks. But then one can also take this encoder and fine-tune it to some other downstream task (an instance of transfer learning). It turns out that the combination of task-general pre-training using free-to-cheap ordinary text data and a small amount of task-specific fine-tuning using labeled data results in substantial performance gains over what came before. The BERT creators gave away both software and the pre-trained parameters (which would be expensive for an individual or a small academic lab to reproduce on their own), and an entire ecosystem of sharing pre-trained model parameters has emerged. I see this toolkit-development ecosysytem as a sign of successful science.
From my limited perspective, very little has happened since then that is not just more BERTology—that is, exploiting BERT and similar models. The only alternative on the horizon, in the last 4 years now, are pre-trained large language models without the encoder component, of which the best known are the GPT family (now up to GPT-3). These models do one thing well: they take a text prompt and produce more text that seeminly responds to the prompt. However, whereas BERT and family are free to reuse, GPT-3’s parameters and software are both closed source and can only be accessed at scale by paying a licensing fee to Microsoft. That itself is a substantial regression compared to BERT. More importantly, though, the GPT family are far less expressive tools than BERT, since they don’t really support fine-tuning. (More precisely, I don’t see any difficult technical barriers to fine-tuning GPT-style models; it’s just not supported.) Thus they can be only really used for one thing: zero-shot text generation tasks, in which the task is “explained” to the model in the input prompt, and the output is also textual. Were it possible to simply write out, in plain English, what you want, and then get the output in a sensible text format, this of course would be revolutionary, but that’s not the case. Rather, GPT has spawned a cottage industry of prompt engineering. A prompt engineer, roughly, is someone who specializes in crafting prompts. It is of course impressive that this can be done at all, but just because an orangutan can be taught to make an adequate omelette doesn’t mean I am going to pay one to make breakfast. I simply don’t see how any of this represents an improvement over the BERT ecosystem, which at least has an easy-to-use free and open-source ecosystem. And as you might expect, GPT’s zero-shot approach is quite often much worse than what one would obtain using the light supervision of the BERT-style fine-tuning approach.